js判断中文字符串长度和js截取中文字符串

//获取字符串长度<br />String.prototype.strLen = function() {  
    var len = 0;  
    for (var i = 0; i < this.length; i++) {  
        if (this.charCodeAt(i) > 255 || this.charCodeAt(i) <) len += 2; else len ++;  
    }  
    return len;  
}  
//将字符串拆成字符，并存到数组中  
String.prototype.strToChars = function(){  
    var chars = new Array();  
    for (var i = 0; i < this.length; i++){  
        chars[i] = [this.substr(i, 1), this.isCHS(i)];  
    }  
    String.prototype.charsArray = chars;  
    return chars;  
}  
//判断某个字符是否是汉字  
String.prototype.isCHS = function(i){  
    if (this.charCodeAt(i) > 255 || this.charCodeAt(i) <)   
        return true;  
    else  
        return false;  
}  
//截取字符串（从start字节到end字节）  
String.prototype.subCHString = function(start, end){  
    var len = 0;  
    var str = "";  
    this.strToChars();  
    for (var i = 0; i < this.length; i++) {  
        if(this.charsArray[i][1])  
            len += 2;  
        else  
            len++;  
        if (end < len)  
            return str;  
        else if (start < len)  
            str += this.charsArray[i][0];  
    }  
    return str;  
}  
//截取字符串（从start字节截取length个字节）  
String.prototype.subCHStr = function(start, length){  
    return this.subCHString(start, start + length);  
}<br /><br /><br />转：http://blog.csdn.net/clh604/article/details/8278303